As is well known to those skilled in the art, many automatic transmissions include control systems capable of controlling various electronically operated solenoid-actuated valves to engage various drive mechanisms of the transmission.
Currently, there exists an automatic transmission system having a fully "adaptive" control system. A thorough discussion of such a transmission control system in contained in U.S. Pat. No. 4,998,450 ('450) issued on Mar. 12, 1991 to Nogle and entitled "Neutral Start Switch To Sense Shift Lever Position," which is commonly owned by the assignee of the present application. This patent is hereby incorporated by reference. The transmission control system includes a microcomputer-based controller that receives input signals indicative of engine speed, turbine speed, output speed (vehicle speed), throttle angle position, brake application, predetermined hydraulic pressure, driver selected gear and operating conditions (PRNODDL), engine coolant temperature, and/or ambient temperature. This controller generates command or control signals for causing the activation of a plurality of solenoid-actuated valves that regulate the application and release of pressure to and from the frictional units of the transmission system.
The '450 transmission control system further discloses a neutral start switch for sensing the position of a manually operated shift lever to select between a plurality of predetermined operating modes. With reference to FIGS. 4B and 19 of the '450 patent, a plate member moves in response to a shift lever and provides a cam surface at the edge with electrically conductive and non-conductive areas. A pair of separate sensors is mounted in the transmission such that an electrical contact pin of each sensor communicates with the cam surface. The signal from the electrical contact pin of each sensor combine to generate a binary code indicative of the shift lever position. Each sensor has a first contact and a second contact. The first contact travels on the cam surface while the second contact closes whenever the first contact is extended with a groove. However, this technique eliminates some of the possible binary code combinations since the first contact generally does not conduct with the second contact closed. Consequently, changes between some of the manual shift lever operating positions involve single bit changes between the respective binary code combinations.
An attempt has been made to resolve these problems by providing a sensing system capable of generating combinations of binary codes which require two or more bit changes between any selected operating modes and further capable of improving the transition codes between the operating modes of the transmission. A thorough discussion of such a transmission sensing system is contained in U.S. Pat. No. 5,325,083 ('083) issued on Jun. 28, 1994 to Nassar et al. and entitled "Manual Valve Position Sensing System," which is commonly owned by the assignee of the present application. This patent is hereby incorporated by reference.
With reference to FIGS. 3 and 6 of the '083 patent, the sensing system includes a plate member that moves in response to the shift lever and includes a cam surface at the edge with electrically conductive and non-conductive areas. An electrical sensor unit is mounted in the transmission in a position to communicate with the contact surface of the plate member. Four electrical contact pins engage the conductive and nonconductive areas on the plate member and generate a binary code having combinations thereof that represent each of the shift lever positions. The binary code combinations are provided for the operating modes and require at least a two-bit change between any two operating modes. In addition, transition codes are provided between each of the operating modes. More particularly, with reference to FIG. 4 of the '083 patent, the sensing system includes three unique transition codes T1, T2, T3 to enable a controller to anticipate and detect transitions between given operating modes. However, this technique fails to independently detect the direction of shift lever movement. For example, transition code T2 occurs on either side of neutral (N) and transition code T3 occurs on either side of drive (D). Therefore, the controller is unable to anticipate whether the shift lever is moving from neutral (N) to reverse (R) or to overdrive (OD). Similarly, the controller is unable to anticipate whether the shift lever is moving from drive (D) to overdrive (OD) or to low (L).
Moreover, the above sensing system may not afford maximum protection against incorrect operating mode detection due to "pin bounce" or pin failure. Pin bounce is defined, for purposed of this patent application, as the momentary disengagement of a contact pin with the conductive or non-conductive areas of the plate member. This pin bounce may occur as a result of engine vibration or various other shock inputs. The pin bounce and pin failure cause the controller to detect an incorrect operating or transition code. Consequently, controller logic must be programmed to detect and ignore these false codes, which increases the complexity and cost of the sensing system.
Accordingly, there exists a need in the relevant art to provide a sensing system capable of generating combinations of binary code that overcomes the disadvantages of the prior art. Furthermore, there exists a need in the relevant art to provide unique transition codes between each of the operating modes of the transmission.